The treatment of waste, whether generated through municipal collection systems or through a broad range of industries, may be observed to vary from simple land fill techniques to somewhat sophisticated chemical and biochemical conversion methods. With the latter methods, significant capital commitments generally are called for which require justification by virtue of environmental protection requirements and/or the generation of profitable by-products.
Controlled composting procedures are considered to offer significant promise for providing for an improved disposal of biodegradable industrial and municipal wastes while generating a somewhat valuable compost designated by-product. To develop a value for that compost by-product, however, it is necessary that economical procedures be provided to achieve a uniform, optimum level of digestion or biodegradation thereof as well as to assure its immunity from deleterious pathogens and the like.
The more primitive of the compositing procedures utilize, for instance, simple windrowing manipulation of waste material, while more sophisticated digestive systems heretofore proposed look to multi-phase procedures of controlled decomposition. For instance, in one arrangement, as disclosed in U.S. Pat. No. 2,820,703, the waste materials are caused to undergo a fungal mold action, following which a period wherein decomposition is predominantly carried out by bacteria active in a mesophilic phase at temperatures below 45.degree.-50.degree. C is effected. Generally following such a phase, a period of maximum biodegradation is permitted to ensue wherein bacteria in the thermophilic phase at temperatures of about 45.degree.-50.degree. C are witnessed. These multi-phase techniques for waste decomposition have been observed to exhibit numerous disadvantages when considered for use in most installations. For instance, more elaborate plant facilities are required, pathogens and the like are present in the noted preliminary digestive phases to engender objectionable odors as well as lead to health control complications, sterilzation of the by-product not being fully assured.
Proposals for overcoming these disadvantages through the utilization of systems operating only in the thermophilic phase and temperature ranges associated therewith have been propagated, see for instance U.S. Pat. No. 3,010,801; 3,138,448, and 3,285,732 by Schulze. Additional approaches to the manyfold problems associated with digestive-type installations are those described in Pierson, U.S. Pat. No. 3,523,012 and Hardy, U.S. Pat. No. 3,114,622. Generally, the difficulties encountered in the development of the systems heretofore proposed appeared to have involved a failure of meeting the biochemical oxygen demand of the digestive process, failure to maintain necessary temperatures to achieve thermophilic phase decomposition as well as failure to derive a practical arrangement for assuring that all particles of the biodegradable waste material are fully treated in a practical manner within the process.
Another aspect of the subject matter resides in the need for developing an aerobic digestive facility capable of generating a reliable compost material by-product for use by smaller industrial and municipal entities. For example, an immediate need for such a facility is present in the cattle raising industry for converting manure and related waste to valuable by-products. Where properly processed, this by-product will retain nutrients permitting its use as a feed supplement for cattle. Thus utilized, the by-product permits a significant lowering of the cost of producing beef. Of course, the facility for digesting such by-products must be operable under conditions of high reliability and must be available at a capital investment commensurate with the development of a profit through by-product utilization.